OBJ files are a popular 3D model file format that is used in various 3D modeling and design software. Opening OBJ files is a simple process, and it allows you to work with 3D models created by others. Here's how to do it:

1. Use 3D Modeling Software: The most common way to open and work with OBJ files is by using 3D modeling software such as Blender, Autodesk Maya, or 3ds Max. These software programs are specifically designed for working with 3D models and support the OBJ file format.

2. Import OBJ File: Once you have the 3D modeling software installed, you can import the OBJ file into the program. This is usually done by selecting the 'Import' option from the file menu and navigating to the location of the OBJ file on your computer.

3. Explore and Edit: After importing the OBJ file, you can explore the 3D model and make any necessary edits or modifications. This could include adjusting the size, shape, texture, or color of the model to fit your needs.

4. Export or Save: Once you're satisfied with the changes you've made to the OBJ file, you can export or save the modified 3D model in the desired format. Most 3D modeling software allows you to export the model as an OBJ file or in other common 3D file formats like STL or FBX.

5. Use Online Converters: If you don't have access to 3D modeling software, you can also use online file converters to open and convert OBJ files. There are various free and paid online tools that allow you to upload an OBJ file and convert it to other formats that you can work with.

Opening and working with OBJ files is essential for anyone involved in 3D modeling, animation, or design. Whether you're creating your own 3D models or collaborating with others, knowing how to open and use OBJ files is a valuable skill to have. With the right software and tools, you can easily import, modify, and export OBJ files to bring your 3D design ideas to life.